Physics

PHOTONICS

Novel and Versatile Mode-locked Fiber Laser Sources
Passively mode-locked fiber lasers have been a hot topic of research in the last two decades primarily for two reasons. Firstly, mode-locked fiber lasers find fruitful applications in various fields such as spectroscopy, imaging, sensing, and many more. Secondly, fiber lasers provide a platform for studying various nonlinear phenomena including soliton dynamics. This work focuses on development of novel and versatile mode-locked fiber lasers in the noise-like pulse regime and also the ability to manipulate their properties, keeping in view specific applications. The aim is to explore the complex physics of formation, interaction and evolution of these pulses and use this knowledge to indigenously develop novel and versatile NLP sources that could be tailor-made for different applications like biosensing, OCT, high resolution spectroscopy and optical communication systems.

Lab-on-a-chip Based Biomedical Sensors
Lab-on-a-chip (LOC) devices are socially relevant in multiple ways. Optofluidics is a micro-fabrication-based technology that explores novel functions and related physics through the synergy between light and fluids at the microscale. Optofluidics lab-on-a-chip technology holds great promise for various fields including bio-photonics, medicine and micromachining applications. One of the main advantages of this field in photonics is the replacement of bulk optics with integrated optics on a chip, which consequently makes the device both time and cost-effective. There are several microfabrication technologies adopted to realize optofluidic devices. Lithographic techniques are extensively used for mass production, but the cost of the reagents involved in the fabrication of the master mold is too high and this limits its potential for design optimization. However, maskless direct writing techniques like femtosecond laser micromachining (FLM) and CO2 laser cutting and engraving technology have an advantage due to their lower fabrication costs and shorter turn-around times (TAT) for chip fabrication. FLM in particular offers added advantages like the capability to produce both optical waveguides and microfluidic channels, the capability to produce 3-dimensional structures, the possibility to combine different fabrication techniques, and the rapid-prototyping capability. We have recently demonstrated FLM for fabricating buried microchannels in fused silica in a much safer way by hot potassium hydroxide (KOH) method when compared to handling highly corrosive hydrofluoric acid. We have also demonstrated the integration of waveguides and microchannels fabricated using FLM in fused silica. Finally, we have demonstrated a highly sensitive novel bimodal interferometric technique in these fused silica chips.

Optical Coherence Tomographyns
We have developed a maneuverable, low-cost, line-field, CMOS camera-based, spectral domain Optical Coherence Tomography (OCT), and demonstrated its use for sensing the nanometer scale vibrations of the human tympanum, in-vivo. A novel Bessel function-based time averaged sampling technique has been developed that can aid in improving the SNR of our low-cost OCT. The potential application of this device for OCT Angiography is also being explored.

Nonlinear Optical Material Characterization
A semi-automated time-resolved third-order nonlinear dynamics characterization facility, utilizing degenerate four-wave mixing, with a 300 femtosecond Ytterbium-doped fiber laser has been set up. This can be used to characterize the response of novel materials that can be used for specific purposes. A fully automated femtosecond Z-scan facility has also been set up to augment the DFWM method.

SERS and Biosensing Applications
Faculty from the department of Physics have been collaborating actively and undertaking interdisciplinary research work on Scientific and societal importance. With the support from our earlier FIST grant (2014), we had set up a Raman microscope facility. This has enabled us to undertake Surface Enhanced Raman spectroscopy application for molecular detection for different chemical & clinical applications. We were successful in fabricating and sensing using novel SERS substrate for detecting biomolecules like Catechol, Dopamine etc., using paper microfluidic platforms. We could phenomenologically explain the origin of these Raman modes using first principle calculations computationally.

NUCLEAR SPECTROSCOPY AND MEDICAL IMAGING

Nuclear structure and Nuclear Spectroscopy (Electron-Gamma Spectroscopy)
The nuclear physics group has rich experience in both theoretical and experimental low-energy spectroscopy. The group carries out studies on level structures of odd-mass and doubly-odd nuclei. Experimental work involving gamma-gamma coincidence and conversion electron spectra are regularly carried out. The nuclear data on level energies, gamma energies and intensities for some of the nuclei differ considerably even for the intense gamma transitions and widely differ from the adopted data in nuclear data sheets. The internal conversion spectrum needs to be studied extensively. Assignment of Multipolarities for some of the transitions need to be relooked. Therefore, an extensive experimental investigation of the gamma and conversion electron spectra to provide precision spectroscopic information has been undertaken. This data would be of great use for calibrating electron detectors and electron transporters.

Design and Optimization of Collimators for Micro-PET and Medical Imaging Simulations
Medical imaging by non-collinear gamma-ray cascade decay may be superior to conventional PET and SPECT. A small animal PET composed of GSO detectors can be adapted to the new modality by retrofitting with a SPECT-like collimator and software modifications. This is an international collaboration work by Prof. Rangachary (University of Saskatchewan, Saskatoon, Canada), Prof. Tomonori Fukuchi (RIKEN Center for Biosystems Dynamics Research, Kobe, Japan) and Leonid Nkuba (University of DSM, Tanzania). The aim is to develop a GATE-based collimated PET model and a custom image reconstruction algorithm.

Development of Intraoperative Multimodal Gamma Camera
The current intraoperative imaging technologies suffer from limitations in their form factor as they are quite bulky to move around in the operation theatre. While some small form factor intraoperative devices exist, they pose challenges due to impaired technical performances (e.g. spatial resolution below 2mm), hindering their efficiency, which subsequently poses a risk to patient safety. An ideal solution to the current problem is a compact device (handheld) with high-performance, real-time multimodal imaging (spatial resolution < 2mm, frame rate > 25 frames/second) and advanced image fusion algorithms designed to improve intraoperative visualization and decision-making.

The research focuses on developing a compact, hand-held device equipped with real-time imaging capabilities and novel image fusion algorithms. This device will integrate:

Detector: CZT detectors offer superior energy resolution allowing to distinguish closely spaced energy peaks and sensitivity compared to traditional scintillators. The direct conversion process in the CZT results in high energy resolution, more than 5% FWHM at 662 keV compared to the typical 7% or higher seen in the scintillators. The CZT functions effectively at room temperature, simplifying the system design, and reducing power consumption, thereby enabling portable detection in intraoperative scenarios.

Fluorescence Imaging: Complementary NIR fluorescence imaging at 850nm with contrast agents such as ICG will provide high-resolution visualization of specific anatomical structures and molecular targets that acts as an aid to the Gamma modality post the navigation.

Optical Imaging: Standard optical imaging will provide anatomical information and aid in the correlation of gamma and fluorescence images in real-time.

Nuclear Reaction Cross-section Measurements
The neutron induced reaction cross section data is important in many areas of nuclear sciences including nuclear medicine, nuclear forensics, nuclear reactors, accelerators, waste transmutations, defense applications, nuclear astrophysics, nuclear structure, and fundamental research. The Researchers at SSSIHL are collaborating with scientists from BARC under a funded project to undertake measurement of neutron cross sections for specific structural materials that are commonly used in current generation nuclear reactors.

A Collaborative & An Exploratory Research Project on Implementation of Deep Learning Techniques for Biomedical/ Radiological Imaging with SSSIHMS & SSSIHL
A joint undertaking between the Departments of Mathematics & Computer Science (DMACS) and the Department of Urology, SSSIHMS, to detect Extra-pulmonary Tuberculosis in CT-based radiological imaging. The Clinical research team has been actively developing a Deep learning-based tool to detect GUTB, which has a unique issue of non-localised growth zones /disease progression, unlike other renal disorders. A new DL-based GUTB detection tool and a user interface module have been developed so clinical users can easily use the DL model for detection. Further data collection and validation are in progress to complete the project.

FUNCTIONAL MATERIALS SCIENCE

Nanoheterostructures and Soft materials (hydrogels) for Gas Sensing applications
Metal oxide semiconductor ZnO thin films are modified by incorporating conducting carbon-black (super C₆₅) through sol-gel process to derive ZnO/C₆₅ heterostructures. ZnO/C₆₅ heterostructure films are tested for different volatile organic compounds (VOCs) gas sensing applications at room temperature. ZnO/C₆₅ films which behaved like n-type semiconductors at low C₆₅ turned out to be p-type like at high fraction of C₆₅ content. ZnO/C₆₅ samples have shown enhanced sensitivity, ultra-fast response and fast recovery times of 5 s and 11 s, respectively at room temperature (28 ^oC). Moreover, Laponite, a synthetic nanosilicate clay and agar, a natural polysaccharide, both imbibe large amounts of water and form into hydrogels. Various physical and chemical stimuli elicit the hydrogel response, which have been applied in designing diverse sensors and biomedical systems. We exploit the change in hydrogel’s ionic conductivity due to volatile organic compounds (e.g. ethanol) interaction with the surfaces of Laponite-Agar hydrogel films. Laponite-Agar gel films have exhibited high selectivity towards ethanol sensing, fast response (4 s) and recovery time (15 s), and limit of detection of 6 ppm at room temperature.

Glasses/Glass-ceramics for Biomedical Applications
Research is focused on developing materials for health and the environment. In this direction, high-density lead-free bismuth borate glasses in binary and ternary bismuth borate glasses have been investigated for radiation shielding applications. High-density bismuth borate glasses possess promising shielding characteristics comparable to the metallic Pb and are much superior to the commercial lead shielding glasses. Moreover, metallic nanocrystals have been embedded in glass matrix using ion-exchange technique and controlled heat treatment process for sensing and biomedical applications. Bioactive and biodegradable borate glasses have been investigated by modifying the glasses with TiO₂ and Ag ions for enhanced therapeutic effects.

Development of Lead-free Ceramic Materials With Enhanced Piezoelectric & Ferroelectric response
Lead-based ceramics, such as Lead zirconate titanate (PZT), have long been the standard for piezoelectric applications due to their excellent electromechanical properties. However, their use poses risks to health and the environment which has been banned by many nations recently. Researchers have been exploring various alternative materials to replace lead-based ceramics while maintaining or even improving their piezoelectric performance. Some of them include Barium titanate (BaTiO₃), Bismuth based ceramics (BiFeO₃), Potassium Sodium Niobate (KNN) etc. Barium Titanate has been a front runner in this material discovery. It is a well-known ferroelectric material with potential for piezoelectric applications. Researchers have explored doping BaTiO₃ with various elements to enhance its piezoelectric properties. For example, doping with rare-earth elements or transition metals can modify the crystal structure and improve piezoelectric performance. Our research group has established a novel BCZT based stoichiometry (Calcium & Zirconium co–doped in Barium Titanate) ceramics with enhanced piezoelectric & ferroelectric response.

Solid-State Electrolytes for Advanced Energy Storage Systems: Development and Optimization
The goal of this research project is to investigate and advance the most recent developments in the field of electro-energy storage. The focus of this research project is energy storage in general, specifically in relation to lithium-ion (Li-ion) and sodium-ion (Na-ion) batteries. The project assesses the energy storage capabilities of new materials for Li/Na-ion batteries as well as designing, fabricating, and characterizing them. We aim to reduce production costs and have as little impact on the environment as possible while improving energy density, cycling stability, and efficiency through innovative techniques and experimental methods. For the past few years, we have been focusing on creating innovative solid electrolytes. Early investigations into the synthesis and testing of solid electrolytes have yielded important information about their viability and possible benefits over liquid electrolytes. The choice of particular materials and fabrication methods has been influenced by these investigations. LiTa₂PO₈ (LTPO) solid electrolyte, which we just fabricated and studied, has extremely promising room temperature conductivity.

Fabrication of Versatile Nanomaterials for Water Remediation, which will Pave the Way for State-of-the-Art Water Purification Technologies
With a zeal to help the local and global populace deal with the colossal challenges of contaminated water, researchers at the Department of Physics have been developing versatile and multifunctional nanomaterials that can simultaneously adsorb multiple contaminants from water, thereby reducing the cost of water purification technology. These tailor-made, novel, and efficient nano adsorbents pave the way for the development of cost-effective water filter prototypes.

Magnetic Nanocomposites for Health and Environment
Our research focuses on developing magnetic polymer nanocomposites with excellent electrical properties, aimed at electromagnetic interference shielding to protect the environment and  human health from electromagnetic pollution. We have synthesized tin-doped magnetite (Sn_xFe_3-xO₄) nanoparticles, through a systematic substitution of Fe²⁺ with Sn²⁺ cations in Fe₃O₄. Using a facile technique of alternate stirring and ultrasonication, we fabricated electroactive-superparamagnetic PVDF-Sn_0.2Fe_2.8O₄ magnetic nanocomposite films. Furthermore, by incorporating conductive materials into the PVDF-Sn_0.2Fe_2.8O₄ nanocomposites, we have enhanced their suitability for EMI shielding applications. These materials exhibit good shielding effectiveness of approximately 99.8%, meeting the shielding effectiveness values mandated by commercial standards. Additionally, we have undertaken the synthesis and characterization of composite systems comprising tin oxide and iron oxide to promote energy sustainability. These materials exhibit moderate magnetism and high dielectric constants (colossal permittivity materials), making them suitable for applications in energy storage and microwave devices

Computational Biophysics
Single molecule detection and sequencing technologies have great importance in understanding of biological processes and have immense potential in various fields including medical diagnostics and personalized medicine. Nanopore-based sequencing has emerged as a promising approach in analyzing the individual molecules directly and offers advantages such as high throughput, rapid analysis, and portability. Biological nanopores like Cytolysin-A, PA63, α-hemolysin etc. offer precise control over pore dimensions and chemical properties. Molecular dynamics (MD) simulations have emerged as indispensable tools for elucidating the fundamental mechanisms underlying nanopore-based single molecule detection and sequencing. In this project, we propose the single molecule detection and DNA/protein sequencing by translocation through protein pores like Cytolysin-A, PA63, α-hemolysin, etc., as well as the synthetic nanopores to elucidate the effect of nanopore properties such as size, charge, and surface chemistry etc using all-atom MD simulations. It allows understanding the microscopic picture of biomolecule translocation, which helps interpret/validate experimental data and predict the performance of nanopore-based sensing platforms. The outcomes of the study have potential implications for biological research and medical diagnostics.